1. Field of the Invention
This invention relates to antifoulants and to a process for inhibiting or preventing fouling in refinery and petrochemical feedstocks during processing. More particularly, this invention relates to inhibiting distillate fuel fouling, manifested by color degradation, particulate formation and gum generation in distillate fuel oils.
2. Description of the Prior Art
During hydrocarbon processing, transportation and storage, the hydrocarbons deteriorate, particularly when subjected to elevated temperatures. The deterioration usually results in the formation of sediment, sludge or gum and can manifest itself visibly by color deterioration. Sediment, sludge or gum formation may cause clogging of equipment or fouling of processing equipment (such as heat exchangers, compressors, furnaces, reactors and distillation systems, as examples). The fouling can be caused by the gradual accumulation of high molecular weight polymeric material on the inside surfaces of the equipment. As fouling continues, the efficiency of the operation associated with hydrocarbon processing equipment such as heat exchangers, compressors, furnaces, reactors and distillation systems decreases. The distillate streams which can result in significant fouling include the straight-run distillates (kerosene, diesel, jet), naphthas, lube oils, catalytic cracker feedstocks (gas oils), light and heavy cycle oils, coker naphthas, resids and petrochemical plant feedstocks.
The precursors leading to the formation of the foulants may form in tankage prior to hydrocarbon processing. Unstable components may include such species as oxidized hydrocarbons (for example, aldehydes and ketones), various organosulfur compounds, olefinic hydrocarbons, various inorganic salts and corrosion products.
Suggestions of the prior art for inhibiting the fouling rate in process heat transfer equipment include U.S. Pat. No. 3,647,677, Wolff et al., which discloses the use of a coke retarder selected from the group consisting of elemental phosphorus and compounds thereof to retard the formation of coke in high-temperature petroleum treatments.
Additionally, U.S. Pat. No. 3,558,470, Gillespie et al., teaches a method of treating mineral hydrocarbon feedstocks subjected to elevated temperatures of the order of 200.degree. to 1300.degree. F. and which have a tendency to form deposits by reason of such heating by adding thereto minor amounts of a certain condensation product of a long chain alkyl or alkenyl monocarboxylic acid, dicarboxylic acid or anhydride thereof, having a number average molecular weight between about 600 and about 5,000, and at least one polyalkylene polyamine and an additional small amount of a certain phosphorous acid or a certain mono-, di- or tri- organic phosphite ester. Of particular interest is U.S. Pat. No. 3,645,886, Gillespie et al., which discloses the use of a certain mixture of a fatty acid ester of an alkanolamine and a certain phosphorous acid or a certain mono-, di-, or tri-organic phosphite ester, to reduce or prevent the fouling of process equipment in petroleum or chemical industries wherein an organic feedstock is subjected to heat exchange at a temperature of from about 200.degree. to about 1300.degree. F.
Also, U.S. Pat. No. 4,024,048, Shell et al., teaches that certain phosphate and phosphite mono- and di-esters and thioesters in small amounts function as antifoulant additives in overhead vacuum distilled gas oils employed as feedstocks in hydrosulfurizing wherein such feedstocks are subjected to elevated temperatures of from about 200.degree. to 700.degree. F. U.S. Pat. No. 4,024,049, Shell et al., teaches that certain thio-phosphate and -phosphite mono- and di-esters in small amounts function as antifoulant additives in crude oil systems employed as feedstocks in petroleum refining which are subjected to elevated temperatures of from about 100.degree. to 1500.degree. F. Furthermore, U.S. Pat. No. 4,024,050, Shell et al., teaches that certain phosphate and phosphite mono- and di-esters in small amounts function as antifoulant additives in crude oil systems employed as feedstocks in petroleum refining which are subjected to elevated temperatures of from about 100.degree. to 1500.degree. F. U.S. Pat. No. 4,024,051, Shell et al., teaches the use of certain phosphorous acids or their amine salts as antifoulants in petroleum refining processes. U.S. Pat. No. 4,226,700, Broom, discloses a method for inhibiting the formation of foulants on petrochemical equipment which involves adding to the petrochemical, during processing, a composition comprising a thiodipropionate and either a certain dialkyl acid phosphate ester or a certain dialkyl acid phosphite ester. Moreover, U.S. Pat. No. 4,425,223, Miller, discloses that hydrocarbon process equipment is protected against fouling during processing of high sulfur-containing hydrocarbon feed stocks by incorporating into the hydrocarbon being processed small amounts of a composition comprised of a certain alkyl ester of a phosphorous acid and a hydrocarbon, surfactant type, sulfonic acid. However, none of these prior art references disclose the unique and effective mixture of a phosphite compound and a carboxylic acid in accordance with the instant invention for inhibiting the degradation, particulate and gum formation of distillate fuel oils prior to and/or during processing.